“One day, dear children, you must die” was not at all popular but it was written by the famed Victorian hymn-composer, John B. Dykes, especially for children, writing tunes to accompany Hymns for Infant Children (1862). As he states in the third person: “He has made it his aim to provide music which—while, if possible, such as shall satisfy the taste of the musician—shall be pleasing and attractive to children” (Preface). This melody, like his for adults such as “Holy, holy, holy,” are lush, even when set to unappealing texts such as this one (writer is anonymous): “Within the grave your limbs must lie,/ And cold and stiff your bodies grow” just “leaves decay,/ And quickly fall beneath your feet” (v. 2). One must therefore learn to be “gentle, humble, meek, and mild….” (v. 3). It would be a difficult hymn to sing for adults or children; fortunately, Dykes’ melody somewhat compensates (listen for the melodic moment in line 3, which sounds like a phrase in Sherman and Sherman’s “Perfect Nanny” from Mary Poppins!)
More discussion on this hymn can be found in Chapter 3, British Hymn Books for Children.